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Year 2 - Theme 2 > Physiology of hearing > Flashcards

Physiology of hearing Flashcards

1
Q

Functions of hearing

A
  • Alerting to dangers
  • Localising objects
  • Recognition
  • Communication via speech
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2
Q

Frequency range of human hearing

A
  • Approx 20-20,000 Hz
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3
Q

What hearing intensity can lead to permanent hearing damage

A

> 90 dB

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4
Q

Bones of the ear

A
  • Malleus
  • Incus
  • Stapes
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5
Q

What does the impedance matching device do

A
  • Increases pressure 45x, by the ratio of tympanic membrane and oval window areas, and to a lesser extent by the lever action of the middle ear ossicles
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6
Q

Purpose of the impedance matching device

A
  • Prevents sound from being reflected back from the fluid-filled cochlea
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7
Q

What is otitis media(and glue ear)

A

• Infection or inflammation of middle ear
○ Usually self-limiting
• Secretory form with effusion
○ “Glue ear”
If chronic causes a conductive hearing loss
○ May need draining
- Grommets

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8
Q

Who are commonly affected by otitis media

A
  • Common in children

- Often from upper respiratory tract infection

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9
Q

What is otosclerosis

A
  • Fusion of stapes with oval window

- Can be fixed by surgery

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10
Q

What is the cochlea

A
  • Is a long, coiled, fluid filled tube
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11
Q

How are the ends of the cochlea tuned

A
  • Basal end is tuned to high frequency sound

- Apical end is tuned to low frequency sounds

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12
Q

Tubes in the cross-section of the cochlear duct

A
  • Scala vestibuli
  • Scala media
  • Scala tympani
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13
Q

What is the scala vestibuli connected to

A
  • Oval window
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14
Q

Feature of scala media

A
  • Is a separate chamber
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15
Q

What is the scala tympani connected to

A
  • Connected to round window
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16
Q

How do the SV and ST communicate

A
  • Via the helicotrema at apex of cochlea
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17
Q

Why do scala vestibuli and scala tympani contain

A
  • Contain perilymph
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18
Q

Content of perilymph

A
  • Extracellular fluid with high Na+ and low K+
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19
Q

What does the scala media contain

A
  • Contains endolymph
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20
Q

Content of endolymph

A
  • Rich in K+ and low in Na+
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21
Q

What is the endolymph produced by

A
  • Stria vascularis
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22
Q

Electrical potential of endolymph

A

+80mV

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23
Q

What is organ of corti

A
  • Is the receptor organ for hearing and is located in the mammalian cochlea
  • This highly varied strip of epithelial cells allows for transduction of auditory signals into nerve impulses’ action potential
24
Q

Location of the organ of corti

A
  • Organ of Corti is located in the scala media of the cochlea of the inner ear between the vestibular duct and the tympanic duct
25
Q

Purpose of the organ of corti

A

The function of the organ of Corti is to transduce auditory signals and minimise the hair cells’ extraction of sound energy

  • Detects the sound induced motions of the basilar membrane
26
Q

What are the types sensory hair cells in the organ of corti

A
  • Inner hair cells

- Outer hair cells

27
Q

What are the apical and basolateral membrane of hair cells bathed in

A
  • Apical membrane of hair cells is bathed in endolymph

- Basolateral membrane of hair cells is bathed in perilymph

28
Q

What are inner hair cells innervated by

A
  • Afferent nerve fibres
29
Q

What are outer hair cells innervated by

A
  • Mainly innervated by efferent nerve fibres
30
Q

How many hair cells are there in each human cochlea

A
  • Only 15,000

- Not regenerated after loss

31
Q

How does mechanotransduction in hair cells occur

A

Deflection of the hair bundle opens non-selective cation channels, the mechano-electrical transducer (MET) channels, at the lower end of the tip links, between neigbouring stereocilia (‘hairs’)
K+, the major cation in endolymph enters and depolarises the hair cell, driven by its electro-(chemical) gradient [the electrical gradients is +120 to +140 mV; there is little or no chemical gradient]; Ca2+ also enters and causes adaptation

  • Voltage gated Ca2+ channels open, Ca2+ triggers vesicle release
32
Q

Effect of Ca2+ release on hair cells

A
  • Afferent nerve fibres are activated
  • Inner hair cells are sensory
  • Outer hair cells are sensori-motor cells
33
Q

Electromotility of outer hair cells

A
  • Outer hair cells amplify basilar membrane motion

- Depolarise - shorten; hyperpolarise - lengthen

34
Q

Effect of prestin

A
  • A modified anion exchanger in the basolateral membrane, is the OHC motor
35
Q

Afferent innervation of the cochlea

A

Neurons in cochlear (spiral) ganglion innervate hair cells and project axons to the brain via the auditory branch of the VIIIth nerve

36
Q

What is each inner hair cell innervated by

A
  • Each inner hair cell is innervated by axons from 10-20 Type I spiral neurons that signal the reception of sound over a wide range of intensities to the brain
37
Q

What are the outer hair cells innervated by

A
  • Outer hair cells are innervated by type II spiral neurons that signal the reception of painfully loud sound that causes cochlear damage to the brain
38
Q

Efferent innervation of the cochlea

A
  • Efferent fibres from the medial olive innervate the outer hair cells directly
  • Efferent fibres from the lateral olive synapse on the type I afferent fibres
39
Q

What does activation of efferent system cause

A
  • Modification of the sensitivity of the cochlea
40
Q

How does noise contribute to sensorineural hearing loss

A
  • Physical effects on hair bundle structure mitochondrial damage, cytotoxic free radicals glutamate excitotoxicity
41
Q

How does ageing cause sensorineural hearing loss

A
  • Ageing(presbyacusis)

- 30% of population over age of 70 have significant hearing loss hair cells, stria vascularis, cochlear ganglion

42
Q

ototoxic drugs that cause sensorineural hearing loss

A
  • Aminoglycoside antibiotics, cisplatin, loop diurectics, salicylate, solvents
43
Q

Sensorineural hearing loss - genetic impact

A

Genetic mutations
• High frequency, 1:2000 of live births
• Syndromic and non-syndromic
• >50 deafness genes identified, 80 additional loci
• ~50% of congenital deafness caused by mutations in
gap junction genes

44
Q

Number of deafness genes identified so far

A

> 50 deafness genes identified

- 80 additional loci

45
Q

What percentage of congenital deafness is caused by mutations

A
  • 50% of congenital deafness is caused by mutations in gap junction genes
46
Q

Targets of deafness genes in the cochlea

A
  • Tight junctions
  • Gap junctions
  • Afferent synapse
  • Tectorial membrane
  • Stria vascularis
  • Transduction complex
47
Q

What are cochlear implants

A
  • Surgically implanted electronic device that provides a sense of sound to a person who is profoundly deaf
48
Q

Results of cochlear implants

A

Results often good enough to recognise and comprehend speech

  • Maximum 24 channels to substitute for 15,000 hair cells
  • Speech is reported to sound ‘robotic’
  • Music sounds awful
49
Q

Central auditory system

A
  • Cochlear nucleus –> superior olivary complex –> nuclei of the lateral lemniscus –> inferior colliculus –> medial geniculate body –> primary auditory cortex
50
Q

Where does parallel processing start

A
  • Cochlear nucleus
51
Q

Type of innervation provided by auditory nerve fibres from cochlear ganglion

A
  • Auditory nerve fibres from cochlear ganglion innervate many types of neuron
  • Neurons extract info about level, onset and timing of sounds
52
Q

What are the two binaural cues used to localise sounds in space in the superior olivary complex

A
  • Interaural level differences are detected in the lateral superior olive(LSO)
  • Interaural time differences are detected in the medial superior olive(MSO)
53
Q

What is the inferior colliculus

A
  • Obligatory synaptic station for all afferents

- Laminar organisation in ICC, iso-frequency sheets

54
Q

Purpose of the inferior colliculus

A
  • Combines complex frequency and amplitude analysis of DCN(dorsal cochlear nucleus)
  • With info on sound localization from SOC(Superior olivary complex)
  • May encode complexity and localization of sounds
  • Auditory reflex centre; reflexive orientation to stimuli
55
Q

Location of the primary auditory cortex

A
  • Primary auditory cortex is located on upper surface of temporal lobe
56
Q

What do lesions in auditory cortex cause

A
  • Lesions in auditory cortex cause defects in: sound localisation, discrimination of temporal pattern, intelligibility of speech
57
Q

What do lesions in broca’s and wernicke’s areas cause

A
  • Impair the production and comprehension of speech

Year 2 - Theme 2 (14 decks)

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